The present invention relates to vehicles, and to measurement of the forces which are exerted by the road on the tires of vehicles.
The present invention also relates to the various electronic assistance devices used, for example, for antilock control of the brakes of a vehicle or antiskid control of the drive wheels, control of the trajectory of a vehicle or other forms of control or monitoring, for instance the pressure of the tires.
In order to control the handling of a vehicle, attempts have been made to determine certain rolling parameters. For instance, in order to reduce the longitudinal slip of the wheels, slip limitation systems (A.B.S., A.S.R.) have been developed which are capable of modulating the torque transmitted to the wheel by the engine or the brake, as a function of the slip derived from the variations in speed of rotation of each wheel. It has also been proposed to measure the torsion (circumferential angular deformation) of the sidewalls of a tire, in order to determine the variations in the torque transmitted to the road. This measurement, which is more direct than derivation from the variation in the speed of rotation, can allow more refined control of the slip limitation systems.
Systems (such as E.S.P.) are also known which influence the brakes or the drive power applied to the wheels, in order to ensure that the trajectory desired by the driver is actually followed by the vehicle. In order to do this, the yaw velocity (velocity of rotation of the vehicle about a vertical axis), the rolling speed, the transverse acceleration of the vehicle and the angular position which the driver applies to the steering wheel, are generally measured simultaneously.